Resin sheets or panels having glass fiber reinforcements are well known in the construction trades and such panels are widely used in the transportation industry as liners for cars and trucks, in food plants, in dairies, and in other industries where there is need for a strong panel which is unaffected by chemicals and resistant to abrasion.
Such panels have been made by passing a glass fiber mat through a bath of thermosetting resin, encasing the glass fiber mat with resin contained therein between top and bottom films and passing this structure between spaced rolls to squeeze out surplus resin and to gauge the thickness of the resulting sheet, after which the sheet is heated to set the resin. One such manufacture is set forth in the Menzer U.S. Pat. No. 2,980,574; another is set forth in my U.S. Pat. No. 3,480,497 and still another is set forth in Menzer U.S. Pat. No. 3,137,601. Another is set forth in Finger U.S. Pat. No. 2,969,301.
Several difficulties were encountered in the practice of these prior methods. A major difficulty was in getting the glass fibers properly oriented and dispersed in the resin. This difficulty became more critical when using loose cut glass fibers instead of a preformed mat of glass fibers. It appeared that while the glass fibers next to the basic resin layer may be properly impregnated with the resin, the fibers farther removed from the resin layer were likely not to be properly impregnated or to be irregularly impregnated, resulting in a poor quality product.
There is set forth in my copending patent application Ser. No. 259,846, now U.S. Pat. No. 3,888,716, an improved method and apparatus which is addressed to the above mentioned difficulties, and in some respects the present application is a continuation of that application, but it also adds major improvements to the manufacture.
In the prior methods of making such panels it has always been necessary to encase the resin layer on both sides with a protective film such as regenerated cellulose. The sticky characteristics of the resin has dictated that the resin be fully protected before being passed through the forming rolls of the machine. Since the protective films are of no benefit to the finished panel they are removed in the course of manufacture and discarded as waste. It would be of great economic value if one of such films could be eliminated. It would also be an advantage if, after being formed and gauged as to thickness, the panel could remain without movement with respect to the structure which supports it until it is cured, thus to eliminate distortion.
Accordingly, I have set myself to the further improvement of the method and apparatus to accomplish the above mentioned objectives. Other objectives and advantages will become apparent as this specification proceeds.